Vessel sealing algorithm and modes

ABSTRACT

A method comprising sealing a vessel residing within tissue between jaws of forceps by sensing an amount of tissue held within the forceps, the sensing by passing electrical current through the tissue by way of the forceps. The method comprises heating the tissue using electrical current, the heating such that impedance of the tissue changes at a first predetermined rate, the first predetermined rate selected based on the sensing. The method comprises desiccating the tissue using electrical current, such that the impedance of the tissue changes at a second predetermined rate different than the first predetermined rate. The method comprises ceasing application of the electrical current to the tissue when impedance of the tissue reaches a predetermined value. Sensing the amount of tissue held within the forceps comprises varying electrical current flowing through the tissue through the forceps such that impedance of the tissue changes at a third predetermined rate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 15/133,854filed Apr. 20, 2016, which claims the benefit of U.S. provisionalapplication No. 62/150,512 filed Apr. 21, 2015, titled “Vessel SealingAlgorithm and Modes,” the contents of which are incorporated herein byreference in their entirety for all purposes.

BACKGROUND

Electrosurgical systems are used by physicians to perform specificfunctions during surgical procedures. Particular systems may be used toperform surgical procedures including sealing vessels residing withintissue. Any advances that increase the amount of control a surgicalinstrument provides during surgical procedures would result in acompetitive advantage.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of exemplary embodiments, reference will nowbe made to the accompanying drawings in which:

FIG. 1 shows a vessel sealing system in accordance with at least someembodiments;

FIG. 2 shows an elevation view of energy based instrument jaws of thevessel sealing system in accordance with at least some embodiments;

FIG. 3 shows an additional elevation view of energy based instrumentjaws of the vessel sealing system in accordance with at least someembodiments;

FIG. 4 shows an electrical block diagram of a controller in accordancewith at least some embodiments;

FIG. 5 shows an example graph depicting an amount of power applied to atissue as well as an impedance of the tissue over time during a sealcycle of the vessel sealing system in accordance with at least someembodiments;

FIG. 6 shows an example graph relating length of a vessel within jaws ofenergy based instrument and power during sensing in accordance with atleast some embodiments;

FIG. 7 shows an example graph relating power during sensing and sealenergy in accordance with at least some embodiments;

FIG. 8 shows an example graph relating power during sensing and sealtime in accordance with at least some embodiments;

FIG. 9a shows an example graph relating a change in impedance of atissue over time undergoing treatment by way of the vessel sealingsystem in accordance with at least some embodiments;

FIG. 9b shows an example graph relating an amount of power applied to atissue over time;

FIG. 10 shows a method in accordance with at least some embodiments; and

FIG. 11 shows a method in accordance with at least some embodiments.

DEFINITIONS

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, different companies may refer to a component by differentnames. This document does not intend to distinguish between componentsthat differ in name but not function.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . .” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first device couples to a second device,that connection may be through a direct connection or through anindirect connection via other devices and connections.

Reference to a singular item includes the possibility that there areplural of the same items present. More specifically, as used herein andin the appended claims, the singular forms “a,” “an,” “said,” and “the”include plural references unless the context clearly dictates otherwise.

Various units, circuit, or other components in this disclosure may bedescribed or claimed as “configured to” perform a task or tasks. In suchcontexts, “configured to” is used to connote structure by indicatingthat the units/circuits/components include structure (e.g., circuitry)that performs those tasks or tasks during operation. As such, theunit/circuit/component can be said to be configured to perform the taskeven when the specified unit/circuit/component is not currentlyoperational (e.g., is not on). The units/circuits/components used withthe “configured to” language include hardware—for example, circuits,memory storing program instructions executable to implement theoperation, etc. Reciting that a unit/circuit/component is “configuredto” perform one or more tasks is expressly intended not to invoke 35U.S.C. § 112(f) for that unit/circuit/component.

“Heating” with respect to tissue shall mean increasing temperature oftissue toward or beyond the boiling point of moisture in the tissue, theincreasing temperature by way of conduction of electrical currentthrough at least some of the tissue. The fact that other portions of thetissue may be heated by convective heat transfer from areas whereconduction takes place shall not obviate the status of “heating.”Moreover, the fact that some desiccation may take place during heatingshall not obviate that heating is taking place regarding the tissue as awhole.

“Desiccation” with respect to tissue shall mean driving off moisture bycontinuing to add energy to the moisture while the moisture is atboiling point. The fact that small pockets of moisture within the tissuemay also be heated to the boiling point (e.g., at the beginning of adesiccation phase) shall not obviate that desiccation is taking placeregarding the tissue as a whole.

“About” in relation to a stated value shall mean the stated value plusor minus 10% (inclusive) of the stated value.

“Seal” or “sealing” with respect to a vessel or group of vessels shallmean a restructuring of the vessel walls in a seal area such that thevessel walls of a vessel are fused together as to become one structurewith no visible lumen and flow through the vessel or group of vessels isblocked. Radio frequency (RF) coagulation, that generally shrinks thevessel wall tissue to reduce the vessel lumen in size while leaving thelumen intact, and may also coagulate blood within and around the vesselto occlude or plug the vessel shall not be considered “sealing” forpurposes of the specification and claims.

“Vessel” shall include any single or bundle of arteries, a single orbundle of veins, or a bundle of both at least one artery and at leastone vein. Additionally, “vessel” may include lymph nodes and ducts. Allof the aforementioned vessels may be isolated or skeletonized or mayalternatively also be in the form of un-skeletonized tissue bundlesincluding both the vessel(s) as previously defined, at least partiallysurrounded and associated with fatty or connective tissue.

All existing subject matter mentioned herein (e.g., publications,patents, patent applications and hardware) is incorporated by referenceherein in its entirety except insofar as the subject matter may conflictwith that of the present invention (in which case what is present hereinshall prevail). The referenced items are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such material by virtue of prior invention.

DETAILED DESCRIPTION

The following discussion is directed to various embodiments of theinvention. Although one or more of these embodiments may be preferred,the embodiments disclosed should not be interpreted, or otherwise used,as limiting the scope of the disclosure, including the claims. Inaddition, one skilled in the art will understand that the followingdescription has broad application, and the discussion of any embodimentis meant only to be exemplary of that embodiment, and not intended tointimate that the scope of the disclosure is limited to that embodiment.

It is to be understood that this invention is not limited to particularvariations set forth herein as various changes or modifications may bemade, and equivalents may be substituted, without departing from thespirit and scope of the invention. As will be apparent to those of skillin the art upon reading this disclosure, each of the individualembodiments described and illustrated herein has discrete components andfeatures which may be readily separated from or combined with thefeatures of any of the other several embodiments without departing fromthe scope or spirit of the present invention. In addition, manymodifications may be made to adapt a particular situation, material,composition of matter, process, process act(s) or step(s) to theobjective(s), spirit or scope of the present invention. All suchmodifications are intended to be within the scope of the claims madeherein.

The various embodiments are directed to vessel sealing methods andrelated vessel sealing systems. In particular, the various embodimentsare directed to a vessel sealing system having multiple modes that areconfigured for various aspects of sealing, such as speed of creating theseal and quality or strength of the seal. For example, one mode ofoperation may reduce the time taken to seal tissue and underlyingvessels within the tissue. Another mode may increase a quality of sealresulting from the procedure but use more time to complete the seal. Themultiple modes of operation are implemented by the surgical device andcontroller.

In various embodiments, a quality of seal may be defined by areliability of a seal. For example, a better quality seal may compriseattributes such as an increased mechanical stability of the seal(increased burst pressure, more force used to peel the walls apart,etc.). In other examples, a quality of seal may be correlated with aseal length, where the seal length extends axially into a vessel. Agreater seal length may correlate with an increased quality of seal.

The controller may enable the surgical device to tune an amount ofelectrical energy applied to targeted tissue containing one or morevessels based on a sensed amount of tissue present within the forceps.During one or more phases of a seal cycle, by way of varying an amountof electrical energy applied to targeted tissue, a controller may beconfigured to control a value of impedance of targeted tissue. That is,the controller may be configured to apply an amount of electrical energyto the targeted tissue such that an impedance of the tissue changes atone or more predetermined rates. It is noted, that although embodimentsmay describe the use of electrical current to control a value ofimpedance, these embodiments are not limited to the use of electricalcurrent but rather a value of impedance may be controlled by way ofmethods implementing voltage control, power control, current control orany combination of the three. It follows, that as a value of impedanceis controlled over time, a rate of change of impedance is alsocontrolled. References to controlling a rate of change of impedance alsorefers to the underlying phenomenon of controlling a value of impedanceof the tissue over time.

During a seal cycle, the ability to control a value of impedance overtime of targeted tissue, enables a physician to treat targeted tissuemore efficiently, reliably and evenly. The ability to treat targetedtissue more efficiently, reliably and evenly is made partially possibleby the ability to control an amount of electrical current applied to thetissue based on a state of the tissue. In contrast, a controller thatdoes not have a similar capability in adapting an amount of electricalcurrent applied to targeted tissue based on a state of the targetedtissue lacks the ability to treat targeted tissue in a comparablemanner. The specification first turns to an illustrative system toorient the reader.

FIG. 1 illustrates a vessel sealing system 100 in accordance with atleast some embodiments. In particular, the vessel sealing system 100comprises an exemplary surgical device 102 comprising forceps 106. Theforceps 106 comprise an elongated shaft that defines a distal endcomprising jaws 108. In various embodiments, jaws 108 may be placedaround tissue so as to grasp and apply a predefined pressure to thetissue. Jaws 108 may also comprise electrodes electrically coupled to anenergy based source (i.e., controller 104), configured to supply energyto the tissue placed between the jaws 108 in a bipolar fashion and treatthe tissue.

The surgical device 102 further defines a handle 110 where a physiciangrips the surgical device 102 during surgical procedures. The handle 110comprises an actuator 112 which a physician may translate in a direction116 to move jaws 108 in respective directions 114 a and 114 b and applya pre-determined grasping and compressing pressure on the targetedtissue between jaws 108. That is, a physician may squeeze the actuator112 closer to the handle 110 to close the jaws 108 and release theactuator 112 to open the jaws 108. Although the example provided in FIG.1 depicts the use of an actuator 112 to open and close jaws 108, anymechanical, electrical, or manual means may be used to open and closejaws 108. Alternate embodiments of surgical devices may include anydevice with opposable jaws that comprise at least one electrode on eachjaw, and include both endoscopic style and open surgery styleinstruments, such as hemostat style devices

The surgical device 102 further comprises a flexible multi-conductorcable 118 housing one or more electrical leads, and the flexiblemulti-conductor cable 118 terminates in a surgical device connector 120.As shown in FIG. 1, the surgical device 102 couples to controller 104,such as by a controller connector 122 on an outer surface of theenclosure 126. Surgical device 102 may deliver electrical current by wayof multi-conductor cable 118 and jaws 108 during a seal cycle of thevessel sealing system.

Still referring to FIG. 1, a display device or interface device 124 isvisible through the enclosure 126 of the controller 104, and in someembodiments a user may select operational modes of the controller 104 byway of the interface device 124 and related buttons 128. For example,using one or more of the buttons 128 the physician may select amongmodes of operation, such as a first mode which may take longer to createthe seal and results in better seal strength. In some embodiments, thefirst mode may provide a more reliable seal across a wide range oftissues. A more reliable seal may be one that is less likely to failwhen tested in the same manner as seals produced by surgical device 102in a different mode. A second mode may seal a vessel in a manner thattakes less time, possibly with lower seal strength. A third mode may beused to seal a vessel faster than the first and second modes, again withpossibly lower seal strength or with a more limited vessel size sealingcapability. The various modes of operation are discussed in more detailbelow. In some embodiments, the mode of operation may be selected byselectively depressing finger buttons present on surgical device 102instead of or in addition to selections made through buttons 128. Fingerbuttons may be present on handle 110, for example. The mode of operationmay also be controlled by a foot pedal assembly 130, discussed next.

In some embodiments, the vessel sealing system 100 comprises the footpedal assembly 130. The foot pedal assembly 130 may comprise a pedaldevice 132, a flexible multi-conductor cable 134 and a pedal connector136. While one pedal device 132 is shown, one or more pedal devices maybe implemented. The enclosure 126 of the controller 104 may comprise acorresponding connector 138 that couples to the pedal connector 136. Aphysician may use the foot pedal assembly 132 to control various aspectsof the controller 104, such as the mode of operation, or on-off controlof the application of electrical current to surgical device 102. Thisembodiment of the surgical device 102 is merely an example and otherembodiments of the surgical device 102 may be used to implement themethods and systems discussed. Various aspects of the jaw 108 at thedistal end of forceps 106 will be discussed next.

FIG. 2 shows a side elevation view of exemplary jaws of the vesselsealing system in accordance with at least some embodiments. Inparticular, jaws 108 comprise a first jaw 204 and a second jaw 206 and afirst and second electrode may be disposed on the first and second jawrespectively, each electrode electrically isolated from each other andcoupled to controller 104 so as to supply energy through the targettissue disposed between the jaws. Alternatively each jaw may define anelectrode, each jaw electrically isolated from each other so as todefine a bipolar device. The second jaw 206 may be stationary while thefirst jaw 204 is rotatable/slidable.

In another embodiment, the second jaw 206 may be stationary while thefirst jaw 206 is rotatable. In yet another embodiment, the forceps 106may be configured in such a way that both the first jaw 204 and secondjaw 206 rotate about a common pivot point between an open orientation(i.e., where the jaws are spaced apart at the distal end of forceps 106)and a closed orientation (i.e., where the jaws are parallel). In yetanother embodiment, jaws 108 may be associated with a blade to cut thetissue, where the blade selectively moves within parallel channelsdefined in each jaw 204 and 206.

Any mechanism or design that enables the jaws 108 to be spaced apart andbrought closer together in an approximate parallel fashion may be used.More particularly jaws 108 may approach each other in such a way thatelectrodes associated with the jaw do not make electrical contact witheach other so that energy flowing from electrodes associated with jaws108 or energized portions of the jaw itself always flows through tissuedisposed through jaws and not directly from one electrode to another.Additionally, any configuration of jaws 108 and associated mechanism maybe used that enables first jaw 204 and second jaw 206 to applysubstantially constant pressure to tissue held between the jaws 108 froma distal to proximate end of the jaws 108. Furthermore, anyconfiguration of jaws 108 that provides for the ability to compressdifferent tissues to a relatively uniform height, such that a gapbetween electrodes is similar across various types of tissues may beimplemented in jaws 108.

FIG. 3, shows a side elevation view of jaws 108 with tissue between thejaws. As depicted, jaws 108 are pressed around tissue 302 comprisingvessels within. In the embodiment depicted in FIG. 3, first jaw 204 isrotatable and slid into place such that a surface 304 abuts tissue 302.As depicted, jaws 108 are positioned to enable sealing of tissue 302and/or blood vessels within tissue 302 by way of an application ofelectrical current administered through the jaws 108 themselves, orthrough electrodes defined on inside surfaces of the jaws. In order toachieve a successful seal in an efficient period of time, a powerapplication algorithm (hereinafter “algorithm”) is applied within thecontroller to determine an amount of electrical current to apply to thetissue 302 by way of jaws 108. In various embodiments, an amount ofelectrical current applied to tissue 302 is varied such that animpedance of the tissue 302 changes at one or more predetermined rates.

In order for the jaws 108 to effectively deliver electrical current totissue 302, jaws 108 may be constructed in a manner such that jaws 108are stiff enough to apply relatively constant pressure across the tissuemass within jaws 108. That is, jaws 108 may be constructed such that asubstantially constant pressure is applied to areas of tissue 302abutting surface 304 and a corresponding surface along second jaw 206.Jaws 108 are constructed in such a manner as to avoid causing shortsacross first jaw 204 and second jaw 206 when first jaw 204 and secondjaw 204 are closed around tissue 302. Overall, jaws 108 are constructedin such a manner that near constant and/or equal pressure is applied totissue held between jaws 108 abutting surface 304 of first jaw 204 and acorresponding surface of second jaw 206.

In various embodiments, as jaws 108 apply substantially constantpressure and deliver electrical current to tissue 302, length 306 oftissue 302 may vary. Although length of tissue within jaws 108 maychange in response to an application of substantially constant pressureand/or electrical current, the length is related to an amount of tissuewithin jaws 108. There may be an initial length of tissue prior to anapplication of substantially constant pressure and/or electricalcurrent, and a length 306 after the application of substantiallyconstant pressure and/or electrical current, but nevertheless length oftissue is correlated to amount of tissue between the jaws 108.

The modes of operation may employ a sealing technology that heats orraises the temperature of tissue located in a seal area (e.g., tissueheld between jaws 108), to a temperature which is above a temperaturethat causes denaturation of structural proteins. During a seal cycle, acombination of pressure and an application of electrical currentresulting in high temperature may cause cellular boundaries to be brokendown in the tissue, and proteins may be denatured. At the end of theseal cycle a seal may be formed by a mixed protein mass. Thus, in a sealcycle a combination of pressure and an application of electrical currentresulting in high temperatures cause a restructuring of tissue in theseal area. It is noted that radio frequency (RF) coagulation shall notbe considered “sealing” for purposes of the specification and claims.

In accordance with example methods, during a seal cycle the tissue 302may undergo three conceptual phases or steps of treatment. The first isa sensing phase, the second is a heating phase, and the third is adesiccating phase. The phases are described according to phenomenaexperienced by the tissue 302 during a phase. For example, during theheating phase, the tissue 302 is heated. Although the seal cycle hasbeen conceptually partitioned into a sensing, heating, and desiccatingphase, it is noted that portions of tissue may be experiencing one ormore of the phenomena identified by the phase descriptors. Such anoccurrence does not negate the fact that tissue 302 may be in a certainphase of treatment. For example, during the sensing phase, portions ofthe tissue may be heated. The fact that some heating takes place doesnot obviate the status of “sensing.” Indeed, in some embodiments, thesecond phase may be initiated during the first sensing phase.

During the sensing phase, an amount of tissue 302 held between jaws 108is sensed. In particular, the jaws 108 may apply an electrical currentthrough tissue 302 between the jaws that is varied by a controller 104(See FIG. 1) such that a value of impedance of tissue 302 is changed atone or more predetermined rates. For example, a value of impedance oftissue 302 may be changed over time such that a rate of change ofimpedance of tissue 302 is about −50 Ohms/second. As such, during anexample sensing phase the impedance of the tissue is driven down at aconstant rate using low power (e.g., less than 5 Watts (W)). An initialdecrease in impedance of tissue 302 may be associated with an increaseof temperature of the tissue 302 and surrounding fluids. Thus, tissue302 may begin to be heated during the sensing phase.

By controlling a value of impedance of tissue 302 over time during thesensing phase, an amount of tissue 302 may be sensed. For example,during the sensing phase, an amount of applied power is controlled toachieve or drive a constant rate of change of impedance of tissue 302.The mean power applied over a duration of time of the sensing phase (toachieve the constant rate of change of impedance) may be indicative ofthe amount of tissue 302 held between jaws 108. Larger amounts of tissuemay use higher mean power to achieve the constant rate of change ofimpedance. Smaller amounts of tissue may use lower mean power to achieveabout the same constant rate of change of impedance.

Thus a value indicating the amount of mean power applied over a durationof time (in conjunction with maintaining a constant rate of change ofimpedance of tissue 302) of the sensing period may be used as an outputvalue to determine the amount of tissue 302 held between jaws 108. Invarious embodiments, a value indicating the amount of mean power applieda duration of time (in conjunction with maintaining a constant rate ofchange of impedance of tissue 302) of the sensing period may also beused as an output value to determine a type of tissue (e.g. vein vs.artery) held between jaws 108.

In other embodiments, applied power may be held constant while the rateof change of impedance is measured over a period of time. The rate ofchange of impedance is then related to the amount of tissue 302 sensedbetween the jaws 108. It is noted that in calculating and measuringimpedance, in one embodiment, the real and imaginary portions of theimpedance are not calculated; but rather, a value indicative of themagnitude of impedance of the tissue is measured at any given timewithout actually determining the underlying components.

Based on the amount of tissue 302 sensed during the sensing phase, aplurality of parameters may be adjusted that are used during the heatingand desiccating phases of the seal cycle. Adjusted parameters mayinclude a targeted value of impedance of tissue at a given time (i.e., aset point impedance as a function of time) or a rate of change ofimpedance of tissue 302 (i.e., a first derivative of impedance as afunction of time). For example, the targeted value of impedance overtime may be defined by a predetermined path or trajectory of theimpedance value over time. Alternatively, the target value of impedancemay be defined by a targeted rate of change of the impedance value overtime. Adjusted parameters may also include an amount of power to applyto tissue 302. Accordingly, controller 104 (FIG. 1) may apply anelectrical current such that the a value of impedance of tissue 302 iscontrolled over time during the heating and desiccating phases based oninformation gathered during the sensing phase and/or a mode of operationselected by the operator.

During the heating phase, a varying electrical current may be applied totissue 302 to drive a change in impedance of tissue 302 at a constantrate, until a lowest value of impedance of the tissue 302 is reached. Insome embodiments, varying electrical current is applied until a lowestvalue of impedance of tissue 302 is reached and surpassed by apredetermined amount. During this heating phase, a change of impedanceof tissue 302 may be controlled by the controller, and may be selectedbased on output information received regarding the amount or type oftissue 302 detected during the sensing phase and/or a mode of operationselected by an operator, such as a physician.

During the heating phase, a temperature of the tissue 302 in jaws 108 isincreased to the boiling point of water or above. The conductivity oftissue 302 is a function of temperature. As the temperature of tissue302 increases, conductivity increases and impedance decreases. As such,a change in impedance of tissue 302 may be used to estimate a change intemperature of the tissue 302. In some embodiments, the boiling pointtemperature may be between 120° C. and 140° C., due to an increasedpressure placed on the tissue 302 by jaws 108.

In various embodiments, the tissue 302 may be heated to a temperaturewhich is above the temperature that causes denaturation of structuralprotein. The combination of pressure applied by jaws 108 and increasedtemperature results in restructuring the tissue in a seal area definedby the portion of tissue 302 held between jaws 108. During the heatingphase, tissue 302 may become thinner, extrusion may occur and tissue mayfold back on itself to create a strong seal or fused portion of vessel.Additionally, some tissue desiccation may occur. The structure of tissue302 created during the heating phase affects the overall seal strengthas well as the reliability of maintaining the seal under pressure.

In controlling the heating rate of tissue 302 or alternatively,controlling the value of impedance of tissue 302 over time, an algorithmcontrolling an amount of electrical current applied by way of jaws 108may account for a plurality of parameters; for example, the amountand/or type of tissue located in the jaws, the conditions of tissue inthe surrounding locality, and the residual heat in the jaws. Because theamount and/or type of tissue located within jaws 108 affects the amountof electrical current needed to raise the temperature, the rate of powerapplied to the tissue is at least partially determined by the amountand/or type of tissue 302 located within jaws 108.

By controlling a value of impedance of tissue 302 over time, whichresults in control of the heating rate of tissue 302 as well, variouspitfalls may be avoided. For instance, if tissue 302 is heated tooquickly, vapor pockets may form which may lead to decreased sealstrength. If the tissue 302 is heated too slowly, the tissue 302 mayhave an acceptable seal, but the sealing time may be too long andexcessive thermal spread may occur. Thus, an algorithm is configured toadjust the value of impedance of tissue 302 over time, which results incontrol of rate of tissue temperature change, versus the overall sealtime in order to achieve a stronger overall seal strength and greaterseal reliability in a relatively short timeframe.

The end of the heating phase is marked by an observation of theimpedance of tissue 302 no longer decreasing and instead the impedanceof tissue 302 beginning to increase. Additionally, at the end of theheating phase, (where a negative rate of impedance change switches to apositive rate of impedance change) a full compression of jaws 108 may bereached in which any tissue extrusion has taken place, and a distancebetween electrodes is determined by the non-electrical standoff heightinside jaws 108. Tissue compression may be correlated to an amount ofimpedance sensed. An increase in impedance may be observed due to thevaporization of water (i.e., water present in the tissue has vaporizedduring the heating), and reformation of proteins. The point at which theimpedance of tissue 302 ceases to decrease and begins to increase marksa transition from the heating phase to the desiccating phase.

During the desiccating phase, the controller 104 may apply a varyingelectrical current by way of jaws 108 to tissue 302 in a manner suchthat a value of impedance of tissue 302 is controlled over a duration oftime, predetermined by an algorithm. In some embodiments, the value ofimpedance of tissue 302 may be changed at a predetermined ratedetermined by an algorithm. In some embodiments, the predetermined ratemay define one or more functions that define a particular trajectory ofan impedance value of tissue 302 over time. For example, a predeterminedrate may define a function that defines a linear trajectory or aparabolic trajectory of an impedance value of tissue 302 over time. Insome embodiments, a predetermined rate may define one or more targetrates of change of impedance value of tissue 302 over time (i.e., atarget rate of change of impedance over time of tissue 302).

The algorithm may set the predetermined rate based on informationgathered during the sensing phase, heating phase and/or a mode ofoperation selected by an operator. The desiccation phase ischaracterized by an upward trend in impedance in which the tissue 302 isreformed under pressure into the fused vessel sealed form. In thedesiccation phase, tissue 302 may be dehydrated and proteins which weredenatured during the heating phase may be recombined during thedesiccation phase. A seal is created by a reformed mixed protein mass.Varying a value of impedance of tissue 302 at a predetermined rateenables the controller 104 to adjust the power delivery to differenttissue types held between jaws 108, thus enabling uniform sealing ofvarious tissues.

Taking into account a sensed amount and/or type of tissue 302 and themode of operation, during the desiccation phase, controller 104 maychange the impedance of tissue 302 based on one or more predeterminedrates, hold the impedance of tissue 302 at a specified predeterminedvalue, or drive the impedance to a certain value within a predeterminedtime frame or a predetermined function of time.

As an example of taking into account a sensed amount of tissue 302 andthe mode of operation, a small, isolated vessel may use a low mean powervalue during the sensing phase, resulting in an activation of a mode ofoperation in which the desiccating phase lasts two seconds with a drivenrate of change in impedance of 300 Ohms per second; by contrast, alarge, well-hydrated tissue bundle may use a larger mean power valueduring the sensing phase, resulting in an mode of operation in which thedesiccating phase lasts four seconds with a driven rate of change inimpedance of 100 Ohms per second.

As described, in various phases of the seal cycle, an amount ofelectrical current to be applied to tissue 304 may be determined by thealgorithm; and the amount of electrical current may be varied accordingto various parameters. For example, the algorithm may adjust an amountof electrical current applied to tissue 302, based on the quantity oftissue determined or sensed between the jaws 108, the composition of thetissue 302 between jaws 108, and hydration levels. In addition, themakeup and condition of tissue 302, such as fat content, collagencontent, and calcification, may be determined and/or considered.

The ability to control a value of impedance of tissue 302 over timeenables the surgical device 102 to produce a better quality seal in anefficient amount of time using an efficient amount of energy. Bycontrolling the value of impedance of the tissue 302 over time duringvarious phases of the seal cycle, the surgical device 102 is able toheat and reform tissue held between jaws 108 evenly and efficientlywhich results in a better seal. As the structure of tissue 302 createdduring the heating phase affects the overall seal strength, thecontrolled application of electrical current to tissue 302 during theheating phase is beneficial. A successful seal may be determined basedon a burst pressure, seal structure, seal speed, extend of spread ofthermal effect to surrounding tissue, vapor formation, the amount oftissue sticking to the applicator, and an amount of unwanted char on thetissue.

By controlling and adjusting the amount of power or electrical currentover a period of time to the tissue 302, stronger sealing of the tissue302 may occur without undertreating the tissue (e.g., the tissue may benon-hemostatic) or over-treating the tissue (e.g., resulting inpotential charring, excessive steam formation, unintended thermal damageto tissue located outside of the jaws, and/or a weaker seal). Additionalaspects of the algorithms that may be applied by the controller 104 arediscussed below, after discussion of an example controller 104.

FIG. 4 shows an electrical block diagram of controller 104 in accordancewith at least some embodiments. In particular, the controller 104comprises a processor 400. The processor 400 may be a microcontroller,and therefore the microcontroller may be integral with read-only memory(ROM) 402, random access memory (RAM) 404, digital-to-analog converter(D/A) 406, analog-to-digital converter (ND) 414, Digital output (D/O)408, and digital input (D/I) 410. The processor 400 may further provideone or more externally available peripheral buses, such as a serial bus(e.g., I²C), parallel bus, or other bus and corresponding communicationmode.

The processor 400 may further be integral with communication logic 412to enable the processor 400 to communicate with external devices, aswell as internal devices, such as display device 124. Although in someembodiments the processor 400 may be implemented in the form of amicrocontroller, in other embodiments the processor 400 may beimplemented as a standalone central processing unit in combination withindividual RAM, ROM, communication, A/D, D/A, D/O, and D/I devices, aswell as communication hardware for communication to peripheralcomponents.

ROM 402 stores instructions executable by the processor 400. Inparticular, the ROM 402 may comprise a software program that, whenexecuted, causes the controller 104 to implement two or more modes ofoperation of the surgical device 102. The RAM 404 may be the workingmemory for the processor 400, where data may be temporarily stored andfrom which instructions may be executed. Processor 400 couples to otherdevices within the controller 104 by way of the digital-to-analogconverter 406 (e.g., in some embodiments the electrical generator 416),digital outputs 408 (e.g., in some embodiments, the electrical generator416), digital inputs 410 (e.g., interface devices such as push buttonswitches 128 or foot pedal assembly 130 (FIG. 1)), and communicationdevice 412 (e.g., display device 124).

Electrical generator 416 generates an alternating current (AC) voltagesignal. Electrical generator 416 may define an active terminal 418 whichcouples to electrical pin 420 in the controller connector 122,electrical pin 422 in the surgical device connector 102, and ultimatelyto jaws 108 (FIG. 3). The active terminal 418 is the terminal upon whichthe voltages and electrical currents are induced by the electricalgenerator 416, and the return terminal 424 provides a return path forelectrical currents. In some embodiments, active terminal 418 may coupleto first jaw 204 (FIG. 2), while return terminal 424 couples to secondjaw 206 (FIG. 2). Thus, electrical generator 416 provides controllableelectrical current to jaws 108. Electrical generator 416 enablescontroller 104 to vary electrical current flowing through tissue 302(FIG. 3) such that impedance of the tissue 302 changes at a given rate.

It would be possible for the return terminal 424 to provide a common orground being the same as the common or ground within the balance of thecontroller 104 (e.g., the common 430 used on push buttons 128), but inother embodiments, the electrical generator 416 may be electrically“floated” from the balance of the controller 104, and thus the returnterminal 424, when measured with respect to the common or earth ground(e.g., common 430) may show a voltage. However, an electrically floatedelectrical generator 416 and thus the potential for voltage readings onthe return terminal 424 relative to earth ground does not negate thereturn terminal status of the terminal 424 relative to the activeterminal 418.

The AC voltage signal generated and applied between the active terminal418 and return terminal 424 by the electrical generator 416 may be RFenergy in the form of a sine wave with variable peak-to-peak voltage; asquare wave with variable peak-to-peak voltage; a square wave with avariable duty cycle; a square wave with variable peak voltage andvariable duty cycle.

In some embodiments, the various modes of operation implemented by thecontroller 104 may be controlled by the processor 400 by way ofdigital-to-analog converter 406. For example, the processor 400 maycontrol the output voltages by providing one or more variable voltagesto the electrical generator 416, where the voltages provided by thedigital-to-analog converter 406 are proportional to the voltages to begenerated by the electrical generator 416. In other embodiments, theprocessor 400 may communicate with the electrical generator 416 by wayof one or more digital output signals from the digital output converter408, or by way of packet-based communications using the communicationdevice 412.

Still referring to FIG. 4, in some embodiments the controller 104further comprises a mechanism to sense the electrical current providedto the tissue within the jaws which enables the controller 104 tomeasure an impedance of the tissue disposed between the jaws. A valueindicative of electrical current provided to the tissue may be providedby current sense transformer 432. In particular, current sensetransformer 432 may have a conductor of the active terminal 418 threadedthrough the transformer such that the active terminal 418 becomes asingle turn primary. Current flow in the single turn primary inducescorresponding voltages and/or currents in the secondary. Thus, theillustrative current sense transformer 432 is coupled to theanalog-to-digital converter 414 (as shown by the bubble A). In somecases, the current sense transformer may couple directly to theanalog-to-digital converter 414, and in other cases additional circuitrymay be imposed between the current sense transformer 432 and theanalog-to-digital converter 414, such as amplification circuits andprotection circuits. For example, in one example system the currentsense transformer 432 is coupled to an integrated circuit device thattakes the indication of current from the current sense transformer 432,calculates a root-mean-square (RMS) current value, and provides the RMScurrent values to the processor 400 through any suitable communicationsystem (e.g., as an analog value applied to the ND 414, as a digitalvalue applied to the multiple inputs of the D/I 410, as a packet messagethrough the communication port 412).

The current sense transformer 432 is merely illustrative of any suitablemechanism to sense the current supplied to the tissue, and other systemsare possible. For example, a small resistor (e.g., 1 Ohm, 0.1 Ohm) maybe placed in series with the active terminal 418, and the voltage dropinduced across the resistor used an indication of the electricalcurrent.

Given that the electrical generator 416 is electrically floated, themechanism to sense current is not limited to the just the activeterminal 418. Thus, in yet still further embodiments, the mechanism tosense current may be implemented with respect to the return terminal424. For example, illustrative current sense transformer 432 may beimplemented on a conductor associated with the return terminal 424.

In some example systems, the feedback parameter used by the processor400 regarding the electrical generator 416 is the electrical currentflow. For example, in systems where the electrical generator canaccurately produce an output voltage independent of the impedance of theattached load, the processor 400 having set point control for thevoltage created by the electrical generator 416 may be sufficient (e.g.,to calculate a value indicative of impedance of the tissue). However, inother cases, voltage too may be a feedback parameter. Thus, in somecases the active terminal 418 may be electrically coupled to theanalog-to-digital converter 414 (as shown by bubble B).

However, additional circuitry may be imposed between the active terminal418 and the analog-to-digital converter 414, for example variousstep-down transformers, protection circuits, and circuits to account forthe electrically floated nature of the electrical generator 416. Suchadditional circuitry is not shown so as not to unduly complicate thefigure. In yet still other cases, voltage sense circuitry may measurethe voltage, and the measured voltage values may be provided other thanby analog signal, such as by way of packet-based communications over thecommunication port 412.

The specification now turns to a more detailed discussion of the variousphases that may occur during a seal cycle. FIG. 5 depicts an examplegraph 500 depicting an amount of power (shown by line 506) applied totissue over time during an example seal cycle. Time is plotted along thex-axis 502 while a power applied to the tissue is plotted along they-axis 504 a. Superimposed in the graph is also a line depicting thechange in impedance over time (shown by line 508) of tissue betweenjaws, values associated with the impedance are shown along a secondy-axis 504 b. Thus, a correlation between the amount of power applied tothe tissue and the change of impedance of the tissue over time may beseen.

The sensing phase 510, is shown approximately in section I; the heatingphase 512 is approximately shown in section II; and the desiccatingphase 514 is shown approximately in section III. Sensing phase 506 isrelatively short and may last approximately 100 milliseconds. Asdepicted on line 506, the sensing phase initially starts using low power(e.g., less that 5 W), however the power level is not limited to amountslower than 5 W. The corresponding line 508 demonstrates that during theapplication of power, the impedance of the tissue is driven down. Thatis, the controller adjusts the power output so as to drive the impedanceof the tissue between jaws down at a constant rate, using low power.Some heating may begin during the sensing phase 506, but the overall aimduring the sensing phase 506 is to sense an amount or type of tissuebetween the jaws.

During the heating phase 512, the amount of power applied over time isincreased. At the end of the heating phase 508, the highest amount ofpower applied may generally coincide with reaching the lowest value ofimpedance of tissue 302. However, the highest amount of power appliedand reaching the lowest value of impedance of tissue 302 may not occurat the same time. The lowest value of impedance of tissue 302 may varybased on the height of electrode separation, type of tissue 302 in thejaws, or an amount of the electrode surface area.

Prior to reaching the lowest value of impedance of tissue between thejaws, an increase in rate of change of power may be used to increase therate of change of the impedance (e.g., to go from −50 Ohms/sec to −100Ohms/sec). Likewise prior to reaching the lowest value of impedance oftissue between the jaws, a decrease in the rate of change of power maybe used to decrease the rate of change of impedance (e.g., to go from−100 Ohms/sec to −50 Ohms/sec). Thus, during the heating phase 512, anapplication of increased power to tissue 302 between the jaws results ina faster drop in impedance. However, the faster the impedance dropsduring the heating phase, the less likely that uniform heating of tissuebetween the jaws occurs. The less likely that uniform heating hasoccurred, the less ideal is the final tissue structure created duringthe heating phase and the less likely one is to achieve a stronger seal.

When the seal cycle transitions from the heating phase 512 to thedesiccating phase 514, there is a reversal of system dynamics betweenheating phase 512 and desiccating phase 514. For example, during theheating phase 512 an increase in the power to the tissue causes theimpedance of the tissue to decrease impedance at a faster rate, while inthe desiccating phase 514 an increase in power causes the impedance toincrease at a faster rate. This reversal of system dynamics results in acontrol structure changing the controller gains. Detecting that tissuehas reached a lowest value of impedance 518 is beneficial as this maydetermine when the control structure changes.

If the detection of the lowest value of impedance 518 occurs too late(e.g., point 520), the output power may increase too quickly and resultin over-desiccation of small quantities of tissue. In situations whereover-desiccation occurs exterior layers of the tissue increases bulkimpedance of the tissue, lowering power output by the controller, andpreventing power application to the durable interior layers of thevessel that benefit from power application as the power application tothe durable interior layers reforms the vessel into a homogenous seal.If the detection occurs too early (e.g., point 522), the system mayreduce the power too quickly, resulting in a longer seal cycle. Thus itis beneficial to determine when a lowest impedance is reached. Invarious embodiments, during the heating phase 512, impedance may becalculated periodically. Due to pockets of moisture and differences intissue type impedance, an impedance of tissue is not necessarily asmoothly varying measurement or value. Thus a controller 104 mayimplement certain methods such as applying an adjustment factor todetermine that a minimum in impedance value has been reached. Use of theadjustment factor may ensure transitions between control structurechanges occur at an appropriate time between the transition from theheating phase 512 to desiccating phase 514.

To determine a point in time to change the control structure, acontroller 104 may identify when the impedance of tissue between jawsstarts to increase. As the impedance decreases during the heating phase512, the controller 104 may track and store the lowest impedanceobserved at point 518. As the impedance begins to increase, thecontroller 104 may compare the most recent measured impedance to thelowest impedance, multiplied by an adjustment factor.

As discussed previously, the impedance of tissue is not necessarily asmoothly varying measurement and thus the impedance of a tissue may beperiodically calculated. The use of the adjustment factor ensures thatthe lowest impedance has been reached before transitioning to thedesiccating phase 514. As impedance may vary at any given time, it maybe difficult to identify when the lowest impedance has been reached. Forexample, a first impedance value measured at a first point in time maybe lower than a second impedance value measured at a second, subsequentpoint in time. However, the second impedance value being higher than thefirst impedance value may not be a good indicator of whether theimpedance of the tissue between the jaws has reached the lowestimpedance and begun an ascending trend. That is, an impedance value mayseem to be rising in a given locality (defined by a narrow window oftime), but a general trend of the impedance value may still bedecreasing. An adjustment factor provides a threshold that a controllermay monitor for before determining that the lowest impedance of a tissuebetween jaws has been reached.

In one embodiment, the adjustment factor may be in the range of 1.1-20.For example, if the controller 104 measures the real part or magnitudeof the minimum impedance to be 30 Ohms, and the adjustment factor is1.5, the controller 104 will change control structures and gains whenthe impedance reaches 45 Ohms (i.e., 30 Ohms*1.5). The adjustment factormay be a function of mode selection or values determined during thesensing phase 510. For example, a larger adjustment factor may be usedin a mode that generates a seal faster than other modes.

After the heating phase 512 ends, the desiccating phase 514 begins(i.e., the impedance of the tissue between the jaws begins to increase).At a time 516 the desiccating phase ends application of power defined aswhen the impedance of tissue reaches a predetermined value. Desiccatingphase 514 is characterized by an upward trend in impedance. Although anupward trend in an approximate linear fashion is depicted in graph 500,any function may be used during any phase of the seal cycle so long asthe value of impedance of the tissue between jaws is controlled. Anyfunction may be used that is effective in producing a good quality seal.

In some embodiments, during the desiccating phase 514, power applied tothe tissue is decreased over time to maintain one or more predeterminedrates of change of impedance of tissue between the jaws. For example, indesiccating phase 514, three different slopes of line 508 may beobserved. From the beginning of desiccating phase 514 to about location524, the rate of change of impedance is at one predetermined rate. Thepredetermined rate may be defined by a predetermined path or trajectoryof the impedance value over time, or the predetermined rate may bedefined as a first derivative of the value of impedance over time. Next,between points 524 and 526, a different predetermined rate may be usedto control a value of impedance of tissue between jaws over time,depicted by a line having a different slope than the previous portionbefore point 524. From point 526 until the end of the desiccating phase514, a third predetermined rate may be used to control the value ofimpedance of tissue between jaws over time.

The end of the desiccating phase 514 may be reached when a determinationis made that the impedance of the tissue has reached a predeterminedvalue. This predetermined value may be determined by feedback sensedduring the sensing phase, or any other prior phase of the respectiveseal cycle. In some embodiments, the application or power may be ceaseddepending on other factors. For example, a final phase may be defined asa period in which zero change in impedance is observed. The impedance oftissue may be driven high and the held at a particular value in order toimplement a slowly tapering application of power. In this example, alength of time (in seconds) may be defined during which there is zerochange of impedance, where the length of time is defined based onparameters collected during earlier phases of the respective seal cycle.

During the desiccating, heating, and sensing phases, in severalembodiments, a predetermined rate may be defined by a set pointimpedance as a function of time, where the set point impedance as afunction of time has the predetermined path or the predetermined rate.The predetermined rate of change may be defined by a predetermined pathfor the portion of line 508 within the desiccating phase 514. In otherembodiments, the predetermined rate may be driven such that a firstderivative of the impedance as a function of time is the predeterminedrate. In various embodiments, the predetermined rates of change may bedetermined based on information gathered during earlier phases of theseal cycle such as the sensing phase 510 or heating phase 512.

In various embodiments, a predetermined rate used during the heating anddesiccating phases may be a factor of sensed variables during thesensing phase of the respective seal cycle. The predetermined rate maybe based on a combination of sensed variables during the sending phaseof the respective seal cycle as well as chosen parameter reflecting amode of operation.

Lesser power is needed further along in the desiccating phase 514 tomaintain a constant rate of change of impedance in the tissue. Duringthe desiccation phase 514, an increase in power applied to tissuebetween the jaws results in a faster increase in impedance of tissuebetween the jaws. An increase of power may be applied to tissue toincrease the rate of change of impedance (e.g., from 50 to 100Ohms/sec).

FIG. 6 shows an example graph 600 relating length of tissue between jawsand power during sensing in accordance with at least some embodiments.Data depicted in FIG. 6 illustrate lab results that confirm thecorrelation between a length of tissue in the jaws (as a proxy foramount of tissue) and power during the sensing phase delivered such thatimpedance changes at a predetermined rate. More specifically, the y-axis604 depicts an amount of power applied to tissue during sensing suchthat a rate of change of impedance in the tissue occurs at −50 Ohms/secover the first 100 milliseconds (i.e., sensing phase). The axis 602shows the length of the tissue held between jaws, where the length ofthe tissue represents the length of the tissue from the distal end tothe proximate end of jaws 108. In other embodiments, the quantity oftissue may be determined by the thickness of the tissue, or by otherdetermined and/or measured characteristics of the tissue.

FIG. 6 confirms a correlation between an amount of tissue and an amountof power that may be used to drive a change of impedance within thetissue bundle over time. For example, a lower amount of power is used todrive a value of impedance over time at a rate of −50 Ohms/sec forsmaller amounts of tissue than what is used for larger amounts oftissue. Such a correlation may be used to determine amount of tissueheld between jaws during a sensing phase of the seal cycle.

FIGS. 7 and 8 illustrate two graphs 700 and 800, respectively, showingdata obtained in one mode of operation of the surgical device 102 (FIG.1). In one example embodiment, graph 700 illustrates sensed Mean Power(in Watts) 702 versus the changes in an amount of delivered seal energy(in Joules) 704. Graph 700 demonstrates a correlation between an amountof power applied during the sensing phase of a seal cycle and an amountof delivered seal energy for respective tissue bundles. That is, themore power used during the sensing phase of the seal cycle of aparticular tissue, the more seal energy delivered to the tissue toachieve the seal. The change in seal energy is a function of the variousparameters that the algorithm adjusts based on the measured mean powerduring the sensing phase.

Similarly, graph 800 illustrates mean power applied during the sensingphase of a seal cycle for respective tissue bundles 802 versus seal time804 (in seconds). Graph 800 demonstrates a correlation between theamount of time used to seal a tissue bundle and the amount of powerapplied during the sensing phase of the seal cycle for that particulartissue. For example, tissue that used more power to drive a change ofimpedance at a predetermined rate also took longer to seal. The changein seal time is a function of the various parameters that the algorithmadjusts based on the measured mean power during the sensing phase. Datacollected for graphs 700 and 800 were obtained during a mode ofoperation that may be similar to a mode 2 as described herein. Asdiscussed previously, the surgical device 102 may operate in variousmodes configured to optimize various aspects and results of the sealcycle as well as the created seal.

The specification now turns to a more detailed description of thevarious modes of operation of the surgical device 102. In some cases,the mode of operation may be set by the surgical device 102 based on adetected or sensed amount of tissue. Alternatively, the mode ofoperation may be selected by an operator. In yet still otherembodiments, the mode may be selected by the controller 104 and thenadjusted by the operator, if needed. Further still, an operator maychoose the mode of operation but the vessel sealing controller 104 mayprovide suggestions or automatically change the mode. For example, ifduring the sensing phase, a determination is made that tissue is toolarge for a successful seal in a mode of operation chosen by theoperator, the controller 104 may automatically switch modes and alertthe physician via a sound or visual indicator on interface device 124(FIG. 1) that a different mode is suggested. In other embodiments, thevessel sealing system 100 may override a mode of operation initiallyselected by the operator.

FIGS. 9a and 9b correspond to each other but show different aspects of aseal cycle performed by the surgical device 102 in three differentmodes. Turning now to FIG. 9a , a graph 900 shows impedances for anexample mode 1 (902) (shown as a solid line), mode 2 (904) (shown as adash-dot line), and mode 3 (906) (shown as a dashed line) overrespective seal cycles. In FIG. 9a , along the x-axis 908, time (inseconds) is shown and along the y-axis 910, impedance values (in Ohms)are shown. FIG. 9b shows an example graph 940 of the power applied totissue during mode 1 (shown as a solid line), mode 2 (shown as adash-dot line and offset slightly to the right so as to be shown moreclearly), and mode 3 (shown as a dashed line) over the respective sealcycle. In graph 940, along the x-axis 942, time (in seconds) is shownand along the y-axis 944, power values (in Watts) are shown. Each of themodes 1, 2, and 3 may begin with a sensing phase comprising similarparameters. In some embodiments, a controller may apply an identicalsensing phase regardless of a mode that the surgical device 102 is beingoperated in. Subsequent to the sensing phase, the controller may thenbranch to a different mode of operation based on readings obtainedduring the sensing phase.

For example, the sensing phases of each of the modes may spend the sameamount of time in the sensing phase, and drive the impedance of thetissue between jaws at about the same rate of change of impedance. Basedon readings obtained during the sensing phase, a controller may thendetermine which mode to operate in. Each of the modes 1, 2, and 3 mayuse information obtained from the sensing phase to adapt parameters usedin the heating and desiccating phases. In mode 1, there is a slower ratechange of impedance during the heating and desiccation phases, and theslower rate of change of impedance increases the total amount of energydelivered to the tissue between jaws; a lower amount of electricalcurrent is applied over a longer time. In mode 3, there is a faster rateof change of impedance in the tissue during the heating and desiccationphases, which enables mode 3 to seal with less energy and shorter time.

With regards to mode 1 in 900, example durations of the sensing, heatingand desiccating phases are shown. For example, duration 912approximately depicts a sensing phase. Duration 914 approximatelydepicts a heating phase of mode 1, and duration 916 depicts adesiccating phase for mode 1. Within desiccating phase 916, a controllermay drive one or more rates of change of impedance of tissue heldbetween jaws. For example, duration 916 a may have one rate of change ofimpedance that is different from a rate of change of impedance duringduration 916 b. Additionally, duration 916 b may have a rate of changeof impedance that is different than rates of changes of impedance duringdurations 916 a and 916 b.

As depicted, mode 1 may have the longest seal cycle. Mode 1 may be usedin situations where a physician is more concerned with hemostasis. Mode1 may be used for tissue bundles, fatty tissues, and large vessels. Sealcycles in mode 1 may be slower and use more energy than modes 2 and 3,however, seals resulting from a seal cycle in mode 1 may be stronger(higher average burst pressure) and more reliable (lower burst pressurestandard deviation and higher reliability). Due to longer seal cycletime, there is more thermal effect and more desiccation. In someembodiments, the time to seal tissue in mode 1 may take 6-9 seconds.

For illustrative purposes some parameters that may be used in mode 1 arediscussed. The heating phase of the seal cycle in mode 1 may target orcontrol the power delivery so as to cause an impedance rate of—(negative) 50 Ohms/sec to gradually raise the temperature of the tissuebetween the jaws, increasing overall power delivery to the tissue duringthis time. During the desiccation phase of the seal cycle in mode 1, therate of change or rate of increase of the impedance of tissue may bevaried between about 50 to 75 Ohms/sec, and the overall desiccationphase may last between about 6 and 8 seconds.

In mode 2 (904), the controller 104 may adapt the heating anddesiccation phases for use with a wider range of tissues. In oneembodiment, a seal cycle performed in mode 2 may last 3 to 5 seconds.Compared to mode 3, mode 2 uses more energy and there is more thermalspread. In one embodiment, during the mode 2, the heating phase drivesimpedance down of tissue 302 between jaws at a rate of 150 Ohms/sec,limiting power that may be used during the heating phase to 150 Watts.In mode 2, during the desiccating phase, the rate of change or increaseof impedance may vary from about 100 Ohms/sec to 300 Ohms/sec as alinear function of the mean power in the sensing phase. The widevariance in change of impedance over time enables the treatment of awider range of tissues during the use of mode 2.

Mode 3 (906) enables an operator to move quickly through tissues wheremaximum hemostasis is not the primary concern, or large vessels are notanticipated. Power applied to the tissue is reduced in mode 3, whileusing less energy to generate the seal. The overall procedure time maybe reduced by using mode 3, resulting in a seal cycle of approximately1-2 seconds. Mode 3 uses the least amount of energy of all three examplemodes, and the heat on the distal end of the jaws 108 (FIG. 1) isreduced compared to the other example modes. There is lower thermalspread (e.g., unwanted thermal damage to adjacent tissues). In someembodiments, use of lower total power may also reduce residualtemperature of the jaws thus reducing the likelihood of latent heatpresent on the jaws that could be dangerous if a physician uses thesurgical device to manipulate unsealed tissue while the surgical deviceis still hot from a previous seal cycle.

In one example, in mode 3, the heating phase may drive the impedance oftissue between jaws down at a rate of −300 Ohms/sec. The allowable powerduring mode 3 is also higher than the other two example modes (e.g., 250W). The change of impedance over time during the desiccating phase inmode 3 is also higher than the other two example modes (e.g., varyingbetween about 150 Ohms to 250 Ohms).

Each seal cycle in mode 3 ends at a uniform impedance threshold, whichmay or may not vary as a function of an amount of power applied duringthe sensing phase or other calculated parameters from the sensing orheating phase. The desiccating phase is also shorter when compared tothe other two example modes. As discussed previously, in some instances,the controller 104 may make a determination that the currently selectedmode is not an efficient or appropriate mode. For example, if anoperator, such as a physician, is using mode 3 on a large tissue bundlewhere a good seal in unlikely to be created, and the power applied tothe tissue during the sensing phase is above a predetermined threshold,the controller 104 may automatically switch over to either mode 2 ormode 3, while alerting the operator. In another embodiment, the operatormay not be alerted and as such a type of automated mode is enabled thatallows switching among the three example modes as determined by thecontroller 104.

Turning now to FIG. 10, an example method is discussed in accordancewith at least some embodiments. The method generates a seal in a tissuethat is held between jaws of a surgical device. In various embodiments,some of the blocks shown in FIG. 10 may be performed concurrently, in adifferent order than shown, or omitted. Additional method elements maybe performed as desired.

Initially an amount of tissue present between jaws is sensed (step1002). As discussed, this might occur during the sensing phase of theseal cycle. During the sensing phase, a value of the impedance of thetissue is changed in a controlled manner. And data collected during thiscontrolled change in impedance of the tissue may be used in subsequentphases in the respective seal cycle to define various parameters used inthe phases of the seal cycle. Next the tissue held between the jaws maybe heated such that the impedance of the tissue changes at a firstpredetermined rate (step 1004). In various embodiments, this might occurduring the heating phase of the seal cycle. During the heating cycle,the impedance of the tissue held between the jaws is driven down at aconstant or predetermined rate.

Next the vessel sealing system may detect that a lowest value ofimpedance of the tissue was reached (step 1006). At this juncture, thevessel sealing system may change control systems in preparation ofbeginning the next phase in the seal cycle. At this step an adjustmentfactor as discussed above, may be used to determine that a lowest valueof impedance of tissue was reached. Next the desiccating phase beginsand the jaws may desiccate the tissue using electrical current such thatimpedance of the tissue changes at a second predetermined rate (step1008). In various embodiments, the impedance of the tissue is driven upat one or more predetermined rates. As discussed previously, apredetermined rate may define one or more functions that define aparticular trajectory of an impedance value of tissue 302 over time. Forexample, a predetermined rate may define a function that defines alinear trajectory or a parabolic trajectory of an impedance value oftissue 302 over time. In some embodiments, the predetermined rate maydefine one or more target rates of change of impedance value of tissue302 over time (i.e., a first derivative of impedance values of tissueover time).

Finally the application of electrical current is ceased when animpedance reaches a predetermined value, determined by parameters sensedearlier in the seal cycle (step 1010). At this point a seal is generatedwithin the tissue held between the jaws.

Turning now to FIG. 11, another example method is discussed inaccordance with at least some embodiments. The method generates a sealin a tissue that is held between jaws of a surgical device based on amode of operation selected as well as an amount of tissue sensed by thesurgical device. In various embodiments, some of the blocks shown inFIG. 11 may be performed concurrently, in a different order than shown,or omitted. Additional method elements may be performed as desired.

Initially, the vessel sealing system may detect of mode of operation ofthe surgical device (block 1102). As discussed previously, the mode ofoperation may optimize various aspects of the seal cycle as well as thegenerated seal. Next an amount of tissue present between jaws is sensed(step 1104). This may occur during the sensing phase of the seal cycle.Next, the surgical device may heat tissue held between jaws of thedevice such that impedance of the tissue changes at a firstpredetermined rate and based on the detected mode of operation (step1106). In various embodiments, this might occur during the heating phaseof the seal cycle. An amount of power applied during step 1106 may belimited based on the detected mode of operation. Additionally, a changeof impedance of the tissue over time may be different depending on thedetected mode of operation.

Next the vessel sealing system may detect that a lowest value ofimpedance of the tissue was reached (step 1108). At this juncture, thevessel sealing system may change control systems in preparation ofbeginning the next phase in the seal system. At this step, an adjustmentas discussed above, may be used to determine that a lowest value ofimpedance of tissue was reached. Next the desiccating phase begins (step1110). At step 1110, the jaws may desiccate the tissue using electriccurrent such that impedance of the tissue changes at a secondpredetermined rate, selected based on the detected mode and the amountof tissue sensed. For example, a change of impedance of the tissue overtime may be different depending on the detected mode of operation.

Finally, the application of electrical current is ceased when impedancereaches a predetermined value (step 1112). In various embodiments theceasing of the application of electric current is determined by analgorithm implemented by way of the controller. At this point a seal isgenerated within the tissue held between the jaws.

From the description provided herein, those skilled in the art arereadily able to combine software with appropriate general-purpose orspecial-purpose computer hardware to create a computer system and/orcomputer sub-components in accordance with the various embodiments andmethods, for example, as discussed with regards to the vessel sealingsystem 100.

References to “one embodiment,” “an embodiment,” “some embodiments,”“various embodiments,” or the like indicate that a particular element orcharacteristic is included in at least one embodiment of the invention.Although the phrases may appear in various places, the phrases do notnecessarily refer to the same embodiment or example.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

We claim:
 1. A method comprising: sealing a vessel residing withintissue between jaws of forceps by: sensing an amount of the tissue heldwithin the forceps, the sensing by controlling the electrical currentdelivered through the tissue by way of the forceps, wherein controllingthe electrical current delivered changes an impedance of the tissue at afirst predetermined rate of impedance change that is constant; selectinga second and a third predetermined rate of impedance change based on theelectrical current required to control the rate of change of impedanceof the tissue at the first predetermined rate of impedance change,wherein the first, second and third predetermined rates of impedancechange are all different from each other; and then heating the tissueusing the electrical current such that the impedance of the tissuechanges at the second predetermined rate of impedance change; and thendesiccating the tissue using the electrical current, the desiccatingsuch that the rate of change of impedance of the tissue changes at thethird predetermined rate of impedance change; and then ceasingapplication of the electrical current to the tissue when impedance ofthe tissue reaches a predetermined value.
 2. The method of claim 1wherein sensing the amount of the tissue held within the forceps furthercomprises: calculating a mean electrical current delivered to the tissueduring the sensing to achieve the first predetermined rate of impedancechange, the mean electrical current delivered during the sensingindicative of the amount of the tissue held within the forceps.
 3. Themethod of claim 2 wherein the first predetermined rate impedance changeis about −50 Ohms/second.
 4. The method of claim 2 wherein controllingthe electrical current flowing through the tissue further comprisesvarying the electrical current flowing through the tissue such that theimpedance of the tissue changes at a rate of about −50 Ohms/second forabout 100 milliseconds.
 5. The method of claim 1 wherein heating thetissue further comprises varying the electrical current through thetissue to drive the second predetermined rate of impedance change tohave a negative slope over the course of the heating.
 6. The method ofclaim 5 wherein the second predetermined rate of impedance change isselected based on the amount of the tissue held within the forceps asdetermined by the sensing.
 7. The method of claim 5 further comprising:detecting a mode selected by an operator, the detecting prior to theheating; and wherein heating further comprises heating the tissue at thesecond predetermined rate of impedance change selected based on theamount of the tissue held within the forceps as determined by thesensing and the mode selected by the operator.
 8. The method of claim 5further comprising transitioning between heating and desiccation basedon at least one selected from the group consisting of: after a lowestvalue of impedance of the tissue is reached; after a rate of change ofimpedance transitions from negative to positive; and after a lowestvalue of impedance of the tissue is reached and surpassed by apredetermined amount.
 9. The method of claim 1 wherein desiccating thetissue further comprises varying the electrical current through thetissue such that the third predetermined rate of impedance change has apositive slope over the course of the desiccating.
 10. The method ofclaim 9 wherein the third predetermined rate of impedance change isselected based on the amount of the tissue held within the forceps asdetermined by the sensing.
 11. The method of claim 1, wherein a sealcycle comprises the sealing, the heating, the desiccating, and theceasing steps; and wherein the predetermined value is determined duringthe seal cycle.
 12. The method of claim 9 further comprising: detectinga mode selected by an operator, the detecting prior to the desiccating;and wherein desiccating further comprises desiccating the tissue at thethird predetermined rate of impedance change selected based on theamount of the tissue held within the forceps as determined by thesensing and the mode selected by the operator.
 13. The method of claim1: wherein desiccating the tissue further comprises varying theelectrical current through the tissue such that the third predeterminedrate of impedance change has a positive slope over the course of thedesiccation; and then further comprising desiccating the tissue usingelectrical current such that the impedance of the tissue changes at thethird predetermined rate of impedance change having a positive slopedifferent than the slope of the second predetermined rate of impedancechange.
 14. The method of claim 1 wherein desiccating the tissue furthercomprises varying the electrical current through the tissue such thatthe third predetermined rate of impedance change is defined by a setpoint impedance as a function of time, where the set point impedance asa function of time has the second predetermined rate of impedancechange, wherein the third predetermined rate of impedance changecomprises a predetermined path.
 15. The method of claim 1 whereindesiccating the tissue further comprises varying the electrical currentthrough the tissue such that a first derivative of the impedance as afunction of time is the third predetermined rate of impedance change.16. A method comprising: sealing a vessel residing within tissue betweenjaws of forceps by: sensing an amount of tissue held within the forceps,the sensing by varying a sense power delivered through the tissue by wayof the forceps such that an impedance of the tissue changes at a firstpredetermined rate of impedance change, the sense power deliveredindicative of an amount of tissue held between the jaws; selecting asecond and a third predetermined rate of impedance change based on thesense power delivered, the first, second and third predetermined ratesof impedance change are all different from each other; and then heatingthe tissue using power, the heating such that the impedance of thetissue changes at the second predetermined rate of impedance change; andthen desiccating the tissue using power, the desiccating such that therate of change of impedance of the tissue changes at the thirdpredetermined rate of impedance change; and then ceasing application ofpower to the tissue when impedance of the tissue reaches a predeterminedvalue.
 17. The method of claim 16 wherein sensing the amount of tissueheld within the forceps further comprises: calculating a mean sensepower delivered to the tissue to achieve the first predetermined rate ofchange of impedance, the mean sense power indicative of the amount ofthe tissue held within the forceps.
 18. The method of claim 16 furthercomprising: detecting a mode selected by an operator, the detectingprior to the heating; and wherein heating further comprises heating thetissue at the second predetermined rate of impedance change, selectedbased on the amount of the tissue held within the forceps as determinedby the sensing and the mode selected by the operator.
 19. The method ofclaim 16 further comprising transitioning between heating anddesiccation based on at least one selected from the group consisting of:after a lowest value of impedance of the tissue is reached; after a rateof change of impedance transitions from negative to positive; and aftera lowest value of impedance of the tissue is reached and surpassed by apredetermined amount.
 20. A method comprising: sealing a vessel residingwithin a tissue between a pair of jaws of forceps by: sensing an amountof the tissue held within the forceps, the sensing by delivering aconstant sense power through the tissue by way of the forceps, andmeasuring a resultant rate of change of impedance of the tissue;selecting a first and a second predetermined rate of impedance changebased on the resultant rate of change of impedance delivered during thesensing, wherein the first and second predetermined rates of impedancechange are different from each other; and then heating the tissue, theheating such that impedance of the tissue changes at the firstpredetermined rate of impedance change; and then desiccating the tissue,the desiccating such that the rate of change of impedance of the tissuechanges at the second predetermined rate of impedance change; and thenceasing application of power to the tissue when the impedance of thetissue reaches a predetermined value.